A solid oxide fuel cell (SOFC) is known as one type of fuel cell, which has a unit cell constructed such that an electrolyte electrode assembly, including a solid electrolyte that is disposed between an anode and a cathode, is interposed between a pair of separators. In the SOFC, for example, oxide ions (O2−) are generated by ionizing oxygen on the cathode, wherein the O2− ions move toward the anode through the solid electrolyte.
Therefore, in the SOFC, it is highly desired that the ions can move easily through the electrolyte electrode assembly, in order to quickly accelerate a power generation reaction. In other words, ohmic resistance or the like of the electrolyte electrode assembly should be small, whereas the conductance (reciprocal of the resistance value) should be high. For example, it has been attempted to decrease the thickness of a solid electrolyte membrane or an ion exchange membrane in order to improve conductance, in the case that an electrolyte supported type of electrolyte electrode assembly or cell (ESC) is used, in which the solid electrolyte membrane is initially manufactured, and the solid electrolyte membrane is used as a substrate wherein an anode or a cathode is provided on each of the end surfaces thereof.
However, in this case, the strength of the solid electrolyte membrane is small. Therefore, it is feared that the electrolyte electrode assembly may be destroyed if high stresses are applied to the SOFC. For this reason, typically, the thickness of the solid electrolyte in the ESC is not less than 200 μm in order to ensure sufficient strength. As described above, in the case of an ESC, an improvement in conductance while maintaining sufficient strength of the ESC are in a so-called trade-off relationship, wherein it is difficult to establish both improved conductance and sufficient strength.
In view of the above, Japanese Laid-Open Patent Publication No. 2003-346842 suggests a reinforcing rib, which is provided for a thin plate-shaped solid electrolyte membrane. That is, it has been attempted to reduce the ohmic resistance of the solid electrolyte layer by forming the solid electrolyte membrane as a thin plate, whereas the strength of the electrolyte electrode assembly is ensured by means of the reinforcing rib.